Composite laminates are generally made from high-quality starting fabrics. The fabrics are frequently bonded with polyurethane adhesives to produce a laminate.
Polytetrafluoroethylene materials, in particular expanded porous PTFE-membranes, are used in a wide variety of applications in the fabric processing industry. Among others, they are used in composite laminates with conventional textiles, such as polyesters and polyamides, as well as other fabrics and are bonded together by means of a polyurethane adhesive.
As is well known, PTFE is a high-quality product. Therefore it is desirable to reutilize laminates containing high-quality fabrics with PTFE. For this purpose such laminates need to be separated into their pure individual components.
The polyurethane (PUR) adhesives used for lamination are cross-linked and do therefore not react to conventional physical separation methods. Therefore an automatic separation of the laminate can only be achieved if the PUR-layer is chemically degraded and made soluble to such an extent that it is fully released from the fabric or from the fabric and the PTFE layer.
The state of the art includes methods for dissolving cross-linked PTFE. Such methods are described in DE-OS 2362921, DE-OS 2516863 and DE-PS 2738572; the PUR is degraded by means of hydrolysis with water or alcoholysis with bivalent or multivalent alcohols at temperatures around 200.degree. C. Thus viscous polyol-like substances are produced from which PUR can again be synthesized.
As known from DE-OS 2514471 or DE-OS 3131203, polyester can be degraded into low-molecular, soluble or liquid products in this way and under similar reaction conditions. Polyamides, too, are; degradable at temperatures above 200.degree. C. with agents containing hydroxyl-groups, as explained in DD-PS 138472. DD-PS 123915, DD-PS 138472 or DE-OS 3435014 describe the degradation of polyesters, polyamides and polyurethanes, either together or stepwise, into liquid or soluble products.
If these processes were applied to PTFE-laminates, the PTFE-membrane would have to be separated from the product of a viscous polyol-like liquid after the decomposition reaction. This is very complicated because the comparatively smaller quantity of the PTFE-constituent would have to be separated from adhering polyol and cleaned by means of solvents.
There is a need for a process by means which the PTFE-membrane can be separated from the laminated fabric without destroying the components.